466 research outputs found
Recovery of surface orientation from diffuse polarization
When unpolarized light is reflected from a smooth dielectric surface, it becomes partially polarized. This is due to the orientation of dipoles induced in the reflecting medium and applies to both specular and diffuse reflection. This paper is concerned with exploiting polarization by surface reflection, using images of smooth dielectric objects, to recover surface normals and, hence, height. This paper presents the underlying physics of polarization by reflection, starting with the Fresnel equations. These equations are used to interpret images taken with a linear polarizer and digital camera, revealing the shape of the objects. Experimental results are presented that illustrate that the technique is accurate near object limbs, as the theory predicts, with less precise, but still useful, results elsewhere. A detailed analysis of the accuracy of the technique for a variety of materials is presented. A method for estimating refractive indices using a laser and linear polarizer is also given
E-learning in developing countries: suggesting a methodology for enabling computer-aided assessment
Traditional education has shifted towards new methods of teaching and learning through the proliferation of information and communication technologies (ICT). The continuous advances in technology enable the realisation of a more distributed structure of knowledge transfer. This becomes critically important for developing countries that lack the resources and infrastructure for implementing cutting-edge education practices. The two main themes of technology in education for developing countries focus either on aspects of technological support for traditional methods and localised processes, or on the investigation of how such technologies may assist distance learning. Commonly such efforts are threefold, relating to content delivery, assessment and provision of feedback. This paper focuses on issues regarding the implementation of e-learning in developing countries and particularly those aspects of computer-aided assessment (CAA) that could be tailored to satisfy the needs of a limited educational infrastructure. The primary contribution of this paper is a proposed methodology for supporting both formative and summative CAA
Ab-initio calculation of Kerr spectra for semi-infinite systems including multiple reflections and optical interferences
Based on Luttinger's formulation the complex optical conductivity tensor is
calculated within the framework of the spin-polarized relativistic screened
Korringa-Kohn-Rostoker method for layered systems by means of a contour
integration technique. For polar geometry and normal incidence ab-initio Kerr
spectra of multilayer systems are then obtained by including via a 2x2 matrix
technique all multiple reflections between layers and optical interferences in
the layers. Applications to Co|Pt5 and Pt3|Co|Pt5 on the top of a semi-infinite
fcc-Pt(111) bulk substrate show good qualitative agreement with the
experimental spectra, but differ from those obtained by applying the commonly
used two-media approach.Comment: 32 pages (LaTeX), 5 figures (Encapsulated PostScript), submitted to
Phys. Rev.
Clinical risk factors of colorectal cancer in patients with serrated polyposis syndrome: A multicentre cohort analysis
Objective Serrated polyposis syndrome (SPS) is accompanied by an increased risk of colorectal cancer (CRC). Patients fulfilling the clinical criteria, as defined by the WHO, have a wide variation in CRC risk. We aimed to assess risk factors for CRC in a large cohort of patients with SPS and to evaluate the risk of CRC during surveillance. Design In this retrospective cohort analysis, all patients with SPS from seven centres in the Netherlands and two in the UK were enrolled. WHO criteria were used to diagnose SPS. Patients who only fulfilled WHO criterion-2, with IBD and/or a known hereditary CRC syndrome were excluded. Results In total, 434 patients with SPS were included for analysis; 127 (29.3%) were diagnosed with CRC. In a per-patient analysis =1 serrated polyp (SP) with dysplasia (OR 2.07; 95% CI 1.28 to 3.33), =1 advanced adenoma (OR 2.30; 95% CI 1.47 to 3.67) and the fulfilment of both WHO criteria 1 and 3 (OR 1.60; 95% CI 1.04 to 2.51) were associated with CRC, while a history of smoking was inversely associated with CRC (OR 0.36; 95% CI 0.23 to 0.56). Overall, 260 patients underwent surveillance after clearing of all relevant lesions, during which two patients were diagnosed with CRC, corresponding to 1.9 events/1000 person-years surveillance (95% CI 0.3 to 6.4). Conclusion The presence of SPs containing dysplasia, advanced adenomas and/or combined WHO criteria 1 and 3 phenotype is associated with CRC in patients with SPS. Patients with a history of smoking show a lower risk of CRC, possibly due to a different pathogenesis of disease. The risk of developing CRC during surveillance is lower than previously reported in literature, which may reflect a more mature multicentre cohort with less selection bias
Growth and mortality of coccolithophores during spring in a temperate Shelf Sea (Celtic Sea, April 2015)
Coccolithophores are key components of phytoplankton communities, exerting a critical impact on the global carbon cycle and the Earthâs climate through the production of coccoliths made of calcium carbonate (calcite) and bioactive gases. Microzooplankton grazing is an important mortality factor in coccolithophore blooms, however little is currently known regarding the mortality (or growth) rates within non-bloom populations. Measurements of coccolithophore calcite production (CP) and dilution experiments to determine microzooplankton (â€63âŻÂ”m) grazing rates were made during a spring cruise (April 2015) at the Central Celtic Sea (CCS), shelf edge (CS2), and within an adjacent April bloom of the coccolithophore Emiliania huxleyi at station J2.
CP at CCS ranged from 10.4 to 40.4âŻÂ”mol C mâ3 dâ1 and peaked at the height of the spring phytoplankton bloom (peak chlorophyll-a concentrations âŒ6âŻmgâŻmâ3). Cell normalised calcification rates declined from âŒ1.7 to âŒ0.2âŻpmol C cellâ1 dâ1, accompanied by a shift from a mixed coccolithophore species community to one dominated by the more lightly calcified species E. huxleyi and Calciopappus caudatus. At the CCS, coccolithophore abundance increased from 6 to 94 cells mLâ1, with net growth rates ranging from 0.06 to 0.21 dâ1 from the 4th to the 28th April. Estimates of intrinsic growth and grazing rates from dilution experiments, at the CCS ranged from 0.01 to 0.86 dâ1 and from 0.01 to 1.32 dâ1, respectively, which resulted in variable net growth rates during April. Microzooplankton grazers consumed 59 to >100% of daily calcite production at the CCS. Within the E. huxleyi bloom a maximum density of 1986 cells mLâ1 was recorded, along with CP rates of 6000âŻÂ”mol C mâ3 dâ1 and an intrinsic growth rate of 0.29 dâ1, with âŒ80% of daily calcite production being consumed.
Our results show that microzooplankton can exert strong top-down control on both bloom and non-bloom coccolithophore populations, grazing over 60% of daily growth (and calcite production). The fate of consumed calcite is unclear, but may be lost either through dissolution in acidic food vacuoles, and subsequent release as CO2, or export to the seabed after incorporation into small faecal pellets. With such high microzooplankton-mediated mortality losses, the fate of grazed calcite is clearly a high priority research direction
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Measurement of the top pair production cross section in 8 TeV proton-proton collisions using kinematic information in the lepton plus jets final state with ATLAS
A measurement is presented of the inclusive production
cross-section in collisions at a center-of-mass energy of TeV
using data collected by the ATLAS detector at the CERN Large Hadron Collider.
The measurement was performed in the lepton+jets final state using a data set
corresponding to an integrated luminosity of 20.3 fb. The cross-section
was obtained using a likelihood discriminant fit and -jet identification was
used to improve the signal-to-background ratio. The inclusive
production cross-section was measured to be
pb assuming a top-quark mass of 172.5 GeV, in good agreement with the
theoretical prediction of pb. The production cross-section in the fiducial region
determined by the detector acceptance is also reported.Comment: Published version, 19 pages plus author list (35 pages total), 3
figures, 2 tables, all figures including auxiliary figures are available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2013-06
Soccer and homosexuality: the conflicts that lie within the affective game of the coach-adolescent athlete relationship
Discussions regarding homosexuality within a sports context are mediated by emotional nuances, especially in the world of soccer, where practitioners are required to have attributes such as strength, masculinity and aggressiveness. As a consequence, this work aimed to analyze the symbolic representation of homosexual relationships between
adolescent soccer players and their coaches; and, furthermore, to understand the intention behind homoerotic relationships that are established between members of the management team and its players. In this study, researchers used the life history methodology, with participation from three adolescent athletes, ages 14, 15 and 16, and three former athletes, ages 26, 28 and 45, who we called speakers. Based on the collection and analysis of research participantsâ testimonies, homosexual relations were found to have occurred between athletes and coaches, or between athletes and other members of the management team, as a part of a âsocial contractâ that is exclusively linked to their professional objectives. These relationships appear to be purely objective; authentic affective links are absent, due apparently to the transient nature of the athletes in these groups. Too, this context is usually marked by the athleteâs physical and emotional vulnerability, and the agreements he makes within this context are accompanied with moral dilemmas, because such adolescents idealize the coach as a paternal archetype.âFutebol e homossexualidade: Os conflitos que se encontram dentro do jogo afetivo da relação treinador-atleta
adolescente.â As discussĂ”es a respeito da homossexualidade no contexto esportivo sĂŁo mediadas por nuanças emocionais,
especialmente no mundo do futebol que exige de seus praticantes atributos de força, virilidade e agressividade. Por este
motivo este trabalho teve como objetivos diagnosticar existĂȘncia de relaçÔes homossexuais entre atletas adolescentes da
modalidade de futebol e seus técnicos e sua representação simbólica e ainda, compreender a intencionalidade das relaçÔes
homoafetivas que se estabelecem entre componentes da equipe diretiva e os jogadores. Esta pesquisa Ă© de natureza qualitativa
e a tĂ©cnica adotada foi a âhistĂłria de vidaâ e a participação de trĂȘs atletas adolescentes em atividade, com idade de
14, 15 e 16 anos e trĂȘs ex-atletas profissionais, com idades 26, 28 e 45 anos serviram de base metodolĂłgica. A partir da
anålise e tratamento dos depoimentos verificou-se que ocorreram relaçÔes homossexuais nas categorias de base envolvendo
técnico e atleta, ou com outros membros da equipe diretiva, como parte dos contratos sociais, ligados exclusivamente a
objetivos profissionais. Estas relaçÔes parecem ser puramente objetais, nĂŁo parecendo existir vĂnculos afetivos duradouros,
aparentemente, devido à natureza transitória de atletas nesses grupos. Também, nesses ambientes, muitas vezes marcados
pela vulnerabilidade fĂsica e emocional dos atletas, os acertos para as relaçÔes homossexuais sĂŁo permeadas por dilemas
morais, tendo em vista que os atletas adolescentes idealizam o treinador como o arquĂ©tipo paterno ideal.âEl fĂștbol y la homosexualidad: Los conflictos que se encuentran dentro del juego afectivo de la relaciĂłn
atleta-entrenador de los adolescentes.â Las discusiones sobre la homosexualidad en contexto deportivo estĂĄn mediadas por
matices emocionales, sobre todo en el mundo del fĂștbol que exige a sus jugadores atributos como la fuerza, la virilidad y los jugadores. En este estudio, los investigadores utilizaron la metodologĂa de la historia de vida, con la participaciĂłn de
tres atletas adolescentes, con 14, 15 y 16 años, y tres ex atletas con 26, 28 y 45 años, que llamamos âoradoresâ. Basado
en la recogida y anĂĄlisis de testimonios de participantes en la investigaciĂłn, se encontrĂł que las relaciones homosexuales
que se han producido entre los atletas y entrenadores, o entre atletas y otros miembros del equipo de gestiĂłn, son como
parte de un âcontrato socialâ que estĂĄ vinculado exclusivamente a sus objetivos profesionales. Estas relaciones parecen
ser solamente como un objeto; porque a veces no hay vĂnculos afectivos autĂ©nticos, debido aparentemente a la naturaleza
transitoria de los atletas en estos grupos. Demasiado, este contexto es generalmente marcado por la vulnerabilidad fĂsica
y emocional del deportista, y los acuerdos que hace dentro de este contexto se acompañan con dilemas morales, debido
a que tales adolescentes idealizan el entrenador como un arquetipo paterno.
la agresividad. Por lo tanto, este estudio tuvo como objetivo diagnosticar la existencia de relaciones homosexuales entre
adolescentes atletas de fĂștbol y sus entrenadores y la representaciĂłn simbĂłlica de estas relaciones. TambiĂ©n comprender
la intencionalidad de las relaciones homoafetivas que se intercambian entre algunos componentes del equipo directivo y(undefined
What Scattering Tells Us About Chiral Perturbation Theory
We describe a rearrangement of the standard expansion of the symmetry
breaking part of the QCD effective Lagrangian that includes into each order
additional terms which in the standard chiral perturbation theory (PT)
are relegated to higher orders. The new expansion represents a systematic and
unambiguous generalization of the standard PT, and is more likely to
converge rapidly. It provides a consistent framework for a measurement of the
importance of additional ``higher order'' terms whose smallness is usually
assumed but has never been checked. A method of measuring, among other
quantities, the QCD parameters and the quark
mass ratio is elaborated in detail. The method is illustrated
using various sets of available data. Both of these parameters might be
considerably smaller than their respective leading order standard PT
values. The importance of new, more accurate, experimental information on
low-energy scattering is stressed.Comment: RevTeX 62 pages (6 figures not added, request from any author),
IPNO/TH 92-106, PURD-TH-93-0
Climatic significance of the marginalization of Scots pine (Pinus sylvestris L.) c. 2500 BC at White Moss, south Cheshire, UK
Subfossil wood from White Moss, south Cheshire, has become the focus of palaeoenvironmental research employing not only conventional coring, pollen analysis, radiocarbon dating and dendrochronology on pine and oak, but also the exhumation of in situ peat areas and dendroecology of the pine ring-width records. Initial dendrochronological research at the site yielded five pine chronologies dating from 3520 to 2462 cal. BC. These and other data indicate three episodes of pine colonization of the mire in the period between 3643 and 1740 cal. BC. Comparison of the pollen and spore records suggest that pine became marginalized at the site c. 2500 cal. BC after successive episodes of increased wetness, and this may represent a staged response to climatic deterioration. Two oak chronologies were dated by reference to the Belfast and to English oak master chronologies to 3228-2898 BC and 2190-1891 BC, respectively, showing the possible co-existence of pine and oak on the mire for part of the time. Further dendrochronological work on subfossil pine at the site resulted in a chronology (WM4) that was cross-matched with pine from elsewhere in England, and subsequently dated absolutely to 2881-2559 BC. Detailed dendroecological information, such as fire episodes and periods of environmental stress indicated in the tree-ring records, have been assigned, precisely and accurately, to calendar years in prehistory. The detailed data show the potential for both dendroecological and wider palaeoclimatic and palaeoenvironmental information that may become available from prehistoric bog-pine chronologies, which might then permit precise correlation and comparisons of proxy-climate data between sites
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